1. Field of the Invention
The present invention relates generally to equipment used in semiconductor processing. More particularly, the present invention relates to non-contact, in-situ methods of making measurements during semiconductor processing.
2. Description of the Related Art
In the presence of heat, reticles have a tendency to distort. The accuracy with which processes that utilize the reticles are performed is compromised when reticles are distorted. By way of example, the accuracy of masking and/or patterning processes which use reticles may be compromised.
To cool a reticle, a heat exchanger that includes an array of thermoelectric chips (TECs) may be used to carry heat away from the reticle. In order to determine how much heat to remove from the reticle, the surface temperatures of the reticle may be obtained using infrared (IR) radiation sensors. Typically, measuring the temperatures involves substantially separating the TECs from the reticle, e.g., removing the reticle out from underneath the TECs, placing the reticle in the vicinity of a sensor such as an IR sensor, and then measuring the temperature of the reticle. Once the temperature of the reticle is determined, if further cooling of the reticle is desired, the reticle is repositioned underneath the TECs. Ceasing the cooling of a reticle in order to obtain a temperature measurement of the reticle is generally time consuming and, thus, relatively inefficient, particularly when additional cooling may be required.
An air gap generally exists between a TEC, e.g., a TEC of a TEC array, a reticle that underlies the reticle. The air gap generally corresponds to a film of gas between the reticle and the TEC array. In order for a reticle temperature controller to accurately prescribe TEC temperatures within a single exposure-cooling cycle such that a target reticle temperature may be achieved at a pre-determined time in the future, knowledge of the size of an air gap is generally necessary. If the size, e.g., height, of the air gap is not maintained, as the air gap has a relatively high associated thermal resistance, heat conduction within the air gap may not be accurately determined. As a result, the target temperature of a reticle may not be achieved in a single exposure-cooling cycle. Thus, without foreknowledge as to the actual height of an air gap and/or the ability to maintain the height of the air gap, controlling the temperature of the reticle may be difficult in a single exposure-cooling cycle.